1. Field of the Invention
The present invention relates to a platinum temperature sensor comprising a platinum film which is formed on an insulating substrate, and more particularly, it relates to an improvement in an external terminal structure of such a platinum temperature sensor.
2. Description of the Background Art
A platinum temperature sensor comprises a platinum film which is formed on an insulating substrate of alumina, for example. In order to attain high resistance in a platinum temperature sensor with a small size, a platinum film is formed in a meandering pattern on an insulating substrate of a limited size, thereby increasing the line length provided by the platinum film. In order to implement such a meandering pattern, a method, advantageously employed is to form a platinum film extending entirely or substantially over the overall surface of an insulating substrate and then to form grooves in the platinum film to perpendicularly pass through the same, so that the remaining portion of the platinum film meanders along the insulating substrate.
FIG. 7 is a sectional view showing a conventional platinum temperature sensor 10 which is obtained by the aforementioned method.
The platinum temperature sensor 10 comprises an insulating substrate 1 of alumina which is 99.6 % in purity, for example. A platinum film 2 is formed on the insulating substrate 1 by printing, sputtering or vacuum deposition, and grooves 3 are formed in the platinum film 2 by application of a laser beam or by dry etching, so that the remaining portion of the platinum film 2 meanderingly extends on the insulating substrate 1. Thus, the platinum film 2 defines a meandering pattern portion 4 which serves as a resistive circuit, and outlet portions 5 continuously extending from respective ends of the meandering pattern portion 4.
The meandering pattern portion 4 is coated with a glass coating film 6 of borosilicate glass, for example. On the other hand, electrode pads 7 of gold or silver-platinum, for example, are formed on the outlet portions 5 by firing, and lead wires 8 prepared from Pt--Ni clad wires, gold wires or platinum wires, for example, are welded onto the electrode pads 7. In order to ensure fixation of the lead wires 8,.glass coating films 9 are applied to cover the lead wires 8, the electrode pads 7 and the outlet portions 5.
However, the aforementioned conventional platinum PG,4 temperature sensor 10 has the following problems:
Due to employment of the lead wires 8, it is necessary to handle the platinum temperature sensor 10 with the greatest possible care because of the poor tensile strength of the lead wires 8.
Due to the lead wires 8, further, such a platinum temperature sensor 10 cannot be suitably mounted on a highly integrated circuit.